The surveillance of industrial environments in which explosive gases are present requires the use of television cameras or other monitoring apparatus with particular explosion proofing constructional characteristics which both ensure the operation thereof even in the case of explosion and avoid the risk that the apparatus itself will trigger an explosion in the environment such as for example by creating sparks. Clearly, in the most frequent cases, in which the use of movable monitoring apparatus is required (and in particular television cameras), which can be orientated to monitor different regions of the environment, the associated movement systems must also possess explosion-proof characteristics.
In particular, scanning devices for television cameras are known which allow displacement thereof in two planes (typically horizontal and vertical) with predetermined excursions. On a fixed support, for example secured to a wall bracket, there is rotatably mounted an intermediate unit to which, in turn, the body of the television camera is rotatably connected. Within the intermediate unit are housed the drive mechanism which allow rotation of the unit with respect to the support and rotation of the television camera with respect to the intermediate unit.
Clearly, scanning devices of this type require the presence of connection cables between the various movable components, which cables also serve to supply the various components for control of the scanning and for control of the television camera. Known scanning devices have in general the main disadvantage that these cables are disposed outside of the device and hang between the different parts in relative motion. Consequently, not only are the cables exposed to the action of external agents (which may be aggressive, especially in some industrial environments), but, in the specific case of installations in an explosive environment, are also directly exposed to a possible explosion thereby constituting a point of weakness of the explosion-proof assembly.
On the other hand, housing the cables within the scanning device would, if known arrangements were used, require an unacceptable increase in the dimensions of the device itself and would in any event involve the further problem of avoiding twisting of the cables themselves during relative rotation of the different components of the device, with consequent wear and deterioration of the cables and possible compromise of the regular function of the television camera. Finally, these problems are aggravated by the fact that television cameras which operate in industrial environments in which explosive gases are present must be subject to safety rules which require that the television cameras themselves be sealed and isolated from the external environment within a sealed casing constructed in such a way that a possible explosion within the television camera cannot be transmitted to the external environment and vice versa.
Obviously, the sealed casing is provided with a transparent window disposed in front of the lens of the television camera, but, because of the particular environment in which these television cameras operate, the protective window becomes dirty very quickly. In order not to prejudice the efficiency of the television camera it is thus necessary to provide for frequent manual cleaning of the window itself by way of an operator who, therefore, has to work in an extremely dangerous environment.
The object of the present invention is that of overcoming the disadvantages of the known devices described by providing, in particular, an explosion-proof scanning device which is simple and economic to construct, extremely compact and of small dimensions, which can remain operational for a long time without deterioration and is suitable for use in an explosive environment, and which allows the television camera to be enclosed within a sealed casing.
Another object of the invention is to provide an automatic cleaning device for the window of a casing which maintains the efficiency of the television camera for a long time without requiring manual interventions, being at the same time simple and economic to produce and not detrimental to the explosion-proof characteristics of the assembly.